Method for enhancing vertical growth during the selective formation of silicon, and structures formed using same

ABSTRACT

A method of selectively forming contact regions on a substrate having a plurality of exposed regions includes selectively forming a contact region on each of the exposed regions of the substrate. During formation, each contact region has a first growth rate in a first direction and a second growth rate in a second direction. While each contact region is being selectively formed on the respective exposed region, the contact region is heated to increase the first growth rate of the contact region in the first direction relative to the second growth rate of the contact region in the second direction. The first growth rate may be a vertical growth rate and the second growth rate may be a lateral growth rate. The contact may be heated by applying electromagnetic radiation to an upper surface of the substrate and not applying the radiation to the vertical portions of the contact region to thereby increase the vertical growth rate relative to the lateral growth rate. The electromagnetic radiation may be collimated light such as that generated by a scanning laser beam, and the substrate and formed contact regions may be silicon or other suitable materials. This method may be used during the fabrication of MOS transistors in memory devices and other integrated circuits.

TECHNICAL FIELD

[0001] The present invention is related generally to semiconductorprocessing, and more particularly to the selective formation of siliconduring manufacture of a semiconductor device.

BACKGROUND OF THE INVENTION

[0002] During the formation of semiconductor integrated circuits,devices are formed in a semiconductor substrate and interconnected toform a circuit that performs a desired function, such as amicroprocessor for processing data or a memory device for storing data.To interconnect the millions of components contained in many integratedcircuits, connections or “contacts” to each device are formed usingconductive materials such as metal and polysilicon, as will beappreciated by those skilled in the art.

[0003]FIG. 1 is a diagram illustrating several silicon contacts 100,102, 104 that have been selectively formed on a silicon substrate 106using a conventional selective deposition method, such as selectiveepitaxial growth (“SEG”). In an ideal SEG process, the contacts 100-104are selectively formed only on exposed regions 108—112 of the substrate106, respectively, and are not formed on other exposed regions of thesubstrate such as the surfaces of isolation oxide regions 114 and 116.Each of the regions 108-112 typically includes a device (not shown),such as a metal oxide semiconductor (“MOS”) transistor or diode, and thecorresponding contact 100-104 is formed on the region to provide contactto the device. Although the contacts 100-104 and substrate 106 aredescribed as being silicon in the example of FIG. 1, the generalconcepts being discussed apply to other materials as well, as will beunderstood by those skilled in the art.

[0004]FIG. 1 illustrates a potential problem that arises whenselectively forming the silicon contacts 100-104 due to the horizontalor lateral growth 118 of the contacts in the direction indicated by thearrows. In an ideal SEG process, the contacts 100-102 are formed onlythrough vertical growth 120 in the direction indicated by the arrow, andin this way the contacts form only on the exposed regions 108-112 of thesubstrate 106 and not on the isolation oxide regions 114, 116. Due tothe lateral growth 118, however, the contacts 100-104 grow towards eachother and over the isolation oxide regions 114, 116. As illustrated forthe contact 102, the lateral growth 118 results from silicon beingdeposited on an upper surface 122 while also being deposited onsidewalls 124, 126 of the contact during formation, as will beunderstood by those skilled in the art. The contact 102 grows in boththe vertical and lateral directions at the same rate.

[0005] The lateral growth 118 may result in adjacent contactsundesirably touching each other, as indicated by the dotted lines 122between the contacts 100 and 102. When the contacts 100 and 102 touch,an unwanted short circuit occurs and the devices being fabricated maynot operate properly. As the size of devices being formed in integratedcircuits continues to decrease, the distance between adjacent contacts100, 102 and 102, 104 also decreases, making lateral growth 118 aconcern since less lateral growth is required before adjacent contactsshort circuit. While the amount of lateral growth of the contacts 100104can be reduced by forming the contacts for a shorter period of time,this is not a viable in most applications because the contacts must beformed to a desired height H, as indicated for the contact 100. As willbe appreciated by those skilled in the art, the contacts 100-104 mustreach the desired height H, for example, in order to ensure subsequentlayers (not shown) can reliably connect to the contacts to provideelectrical connection to the underlying devices. For example, in a MOStransistor contacts it is desirable that contacts being formed to sourceand drain regions of the transistor are at least as high as a gate stackformed over a channel region of the transistor to ensure subsequentlayers form proper connection to the contacts.

[0006] There is a need for a method of selectively forming siliconcontacts of desired heights in integrated circuits having reduced devicesizes.

SUMMARY OF THE INVENTION

[0007] According to one aspect of the present invention, a method ofselectively forming contact regions on a substrate having a plurality ofexposed regions includes selectively forming a contact region on each ofthe exposed regions of the substrate. During formation, each contactregion has a first growth rate in a first direction and a second growthrate in a second direction. While each contact region is beingselectively formed on the respective exposed region, the contact regionis heated to increase the first growth rate of the contact region in thefirst direction relative to the second growth rate of the contact regionin the second direction. The first growth rate may be a vertical growthrate and the second growth rate may be a lateral growth rate. Thecontact may be heated by applying electromagnetic radiation to an uppersurface of the substrate and not applying the radiation to the verticalportions of the contact region to thereby increase the vertical growthrate relative to the lateral growth rate. The electromagnetic radiationmay be collimated light such as that generated by a scanning laser beam,and the substrate and formed contact regions may be silicon or othersuitable materials. This method may be used during the fabrication ofMOS transistors in memory devices and other integrated circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a diagram illustrating silicon contacts formed on asemiconductor substrate using a conventional selective depositionmethod.

[0009]FIG. 2 is a diagram illustrating a method for selectively formingsilicon contacts on a semiconductor substrate according to oneembodiment of the present invention.

[0010]FIG. 3 is a diagram illustrating a MOS transistor includingcontact formed using the method of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

[0011]FIG. 2 is a diagram illustrating a method for selectively formingsilicon contacts 200, 202, 204 on a semiconductor substrate 206according to one embodiment of the present invention. In the method,collimated electromagnetic radiation 208 is applied to illuminate thecontacts 200-204 during their formation and reduce the lateral growth ofthe contacts by increasing a vertical growth rate of the contactsrelative to a lateral growth rate, as will be described in more detailbelow. Certain details are set forth below to provide a sufficientunderstanding of the invention. However, it will be clear to one skilledin the art that the invention may be practiced without these particulardetails. In other instances, well-known processes, materials, and devicedetails have not been shown in detail in order to avoid unnecessarilyobscuring the invention, but are well within the understanding of thoseskilled in the art.

[0012] The semiconductor substrate 206 includes isolation oxide regions210 and 212 formed between the contacts 200, 202 and the contacts 202,204, respectively. Each of the contacts 200-204 is formed over anexposed region 214-218, respectively, of the substrate 206, with each ofthese regions including a device (not shown), such as a MOS transistor,formed in the substrate within the region. Each of the contacts 200-204is formed according to a selective deposition process so that thecontacts are formed on the exposed regions 214-218 of the substrate 206,and are not formed on the exposed isolation oxide regions 210 and 212.

[0013] The selective deposition of the silicon contacts 200-204 istypically accomplished through a selective epitaxial growth (“SEG”)process, but other selective deposition processes may also be utilized.As will be appreciated by those skilled in the art, during the SEGprocess, the substrate 206 is exposed to a source of silicon, such assilicon tetrachloride SiCl₄, silane SiH₄, or dichlorosilane SiH₂Cl₂,which provides the silicon that is deposited to form the contacts200-204. To make the SEG deposition process selective, chlorine Cl orother suitable compound is present during the formation of the contactsto prevent deposition of the silicon on the isolation oxide regions 210,212 and any other exposed regions except for the exposed regions 214-218of the substrate 206. In some situations, the exposed regions 214-218 ofthe substrate 206 may be openings in an oxide layer formed on thesubstrate.

[0014] During the selective formation of the contacts 200-204, thecollimated electromagnetic radiation 208 is applied to the contacts toheat the horizontal upper surfaces of the contacts, as will be nowdescribed in more detail with reference to the contact 202. The contact202 includes an upper surface 220 that is substantially horizontal orparallel to the upper surface on the silicon substrate 206, and furtherincludes two sidewall surfaces 222 and 224 that are substantiallyvertical or perpendicular to the upper surface of the silicon substrate.The collimated electromagnetic radiation 208 has a direction ofpropagation, as indicated by the arrows, which is substantiallyperpendicular to the surface of the semiconductor substrate 206 and theupper surface 220. A scanning laser or other suitable source maybeutilized to generate the collimated electromagnetic radiation 208, andalthough the radiation is described as being electromagnetic radiation,any directional radiation source that can heat the upper surface 220 bya relatively large amount compared to the sidewall surfaces 222, 224 canbe utilized, as will be discussed in more detail below.

[0015] Because the direction of propagation of the collimatedelectromagnetic radiation 208 incident on the upper surface 220 issubstantially perpendicular to the upper surface, the intensity of theradiation incident upon the upper surface is relatively great, and thusthe upper surface is heated by a relatively large amount due to therelatively high intensity of the applied electromagnetic radiation. Aswill be understood by those skilled in the art, the increasedtemperature of the upper surface 220 results in more silicon beendeposited on the upper surface. Thus, the increased temperature of theupper surface 220 due to the incident radiation 208 increases a verticalgrowth rate 226 of the contact 202 in the vertical direction indicatedby the arrows. At the same time, the intensity of the radiation 208incident upon the sidewall surfaces 222, 224 is relatively smallcompared to the intensity incident upon the upper surface 220. This istrue because the sidewall surfaces 222, 224 are substantially verticalrelative to the upper surface 220 and thus substantially parallel to theapplied collimated electromagnetic radiation 208. As a result, arelatively small portion of the applied collimated electromagneticradiation 208 is incident upon the sidewall surfaces 222, 224, and thusthe surfaces are not significantly heated by the applied radiation. Thesidewall surfaces 222, 224 are thus at a lower temperature relative tothe upper surface 220. The lower temperature of the sidewall surfaces222, 224 results in a lateral growth rate 228 in the horizontaldirection as indicated by the arrows that is relatively small comparedto the vertical growth rate 226.

[0016] In operation of the overall process of selectively forming thecontacts 200-204 illustrated in FIG. 2, the substrate 206 is initiallyprocessed in preparation for forming the contacts, as will beappreciated by those skilled in the art. The SEG process is then startedand the contacts 200-204 begin forming over the regions 214-218,respectively. At the same time, the radiation 208 is applied to beginheating the upper surfaces 222 of the contacts 200-204. The radiation208 need not be applied coincident with the SEG process, but may startbefore or after the process starts. The radiation 208 heats the uppersurfaces 220, causing the vertical growth rate 226 to increase relativeto the lateral growth rate 228, which does not increase significantlybecause the intensity of the radiation on the sidewall surfaces 222, 224is small relative to the intensity on the upper surfaces. As a result,the contacts 200-204 grow at a faster rate in the vertical direction 226than in the lateral direction 228. The relatively smaller lateral growthrate 228 results in less lateral growth of each contact 200- 204 duringthe time the contact is being formed. As a result, the sidewall surfaces222, 224 are more vertical than the sidewalls of contacts formedaccording to the conventional process previously discussed withreference to FIG. 1.

[0017] The reduced lateral growth rate 228 relative to the increasedvertical growth rate 226 enables contacts 200-204 to be selectivelyformed having a desired height H in semiconductor integrated circuitshaving reduced lateral spacing between devices. As seen in the exampleof FIG. 2, the reduced lateral growth of the contacts 200 and 202results in the contacts being formed only slightly over the isolationoxide region 210, while the increased vertical growth rate 226 enablesthe contacts to be grown to the desired height H. In FIG. 2, thesurfaces that are significantly heated by the applied radiation 208 areindicated via the thicker lines and are seen to include the top surfacesof the isolation oxide regions 210 and 212 in addition to the uppersurfaces 220. It should be noted that only the upper surfaces 220 of thecontacts 200- 204 are heated by the applied radiation 208 so that anydopants contained in the regions of devices underlying the contacts donot diffuse due to the heat. Such diffusion could destroy shallowjunction devices, as will be appreciated by those skilled in the art.Although the example of FIG. 2 includes silicon contacts 200-204 and asilicon substrate 206, other materials such as gallium arsenide GaAs andsilicon germanium SiGe may also be utilized, as will be appreciated bythose skilled in the art.

[0018]FIG. 3 is a diagram illustrating a MOS transistor 300 formed in asemiconductor substrate 302, the MOS transistor including contacts 304,306 formed according to the method of FIG. 2. In the example of FIG. 3,the MOS transistor is an NMOS device including an N+ source region 308and N+ drain region 310, with a P-type channel 312 being defined betweenthe source and drain regions. A gate stack 314 is formed on thesubstrate 302 over the channel region 312. The gate stack includes anoxide layer 316, polysilicon layer 318, silicide layer 320, oxide layer322, and nitride passivation layer 324 formed as shown. The layers 316-324 in the gate stack 314 result in the stack having a height H, and thecontacts 304, 306 are formed having at least the height H to enablereliable connection to the contacts via subsequently formed layers. Aninsulating spacer layer 326, such as a silicon nitride or silicone oxidelayer, is disposed on both sides of the gate stack 314 between the gatestack and the contacts 304, 306 to isolate the conductive layers in thestack from the contacts.

[0019] In operation, a gate voltage is applied to the polysilicon layer318 to induce a channel in the channel region 312, causing current toflow through the contact 306, through the drain region 310 and throughthe channel region to the source region 308, and through the sourceregion to the contact 304, as will be appreciated by those skilled inthe art.

[0020] It is to be understood that even though various embodiments andadvantages of the present invention have been set forth in the foregoingdescription, the above disclosure is illustrative only, and changes maybe made in detail, and yet remain within the broad principles of theinvention. For example, many of the components described above may beimplemented using different materials and different conductivity types.Therefore, the present invention is to be limited only by the appendedclaims.

1. A method of selectively forming contact regions on a substrateincluding a plurality of exposed regions, the method comprisingselectively forming a contact region on each of the exposed regions ofthe substrate, each contact region being formed having a first growthrate in a first direction and a second growth rate in a seconddirection, and while each contact region is being selectively formed onthe respective exposed region, heating the contact region to increasethe first growth rate of the contact region in the first directionrelative to the second growth rate of the contact region in the seconddirection.
 2. The method of claim 1 wherein the substrate comprises asilicon substrate and each of the contact regions comprises a siliconregion.
 3. The method of claim 2 wherein each of the silicon regionscomprises an epitaxial region.
 4. The method of claim 1 wherein thefirst direction corresponds to a vertical direction that issubstantially perpendicular to a surface of the substrate and the seconddirection corresponds to a lateral direction that is substantiallyparallel to the surface of the substrate.
 5. The method of claim 1wherein the method further comprises forming an insulating layer on thesubstrate and removing portions of the insulating layer to form theexposed regions of the substrate.
 6. The method of claim 1 whereinheating the contact region comprises illuminating a portion of thecontact region with electromagnetic radiation to increase thetemperature of the portion of the contact region relative to the otherportions of the contact region.
 7. The method of claim 6 wherein theportion of each contact region comprises an upper surface and the otherportions of the contact regions comprise sidewall surfaces, the sidewallsurfaces being substantially perpendicular to the upper surface, and theelectromagnetic radiation having a direction of propagation that issubstantially perpendicular to the upper surface and parallel to thesidewall surfaces to illuminate the upper surface and substantially notilluminate the sidewalls so that the temperature of the upper surfaceincreases relative to the temperature of the sidewalls.
 8. The method ofclaim 6 wherein illuminating the portion of the contact region withelectromagnetic radiation comprises applying collimated light to theportion.
 9. The method of claim 8 wherein the collimated light comprisesa scanning laser beam applied to the portion.
 10. The method of claim 1wherein heating the contact starts at substantially the same time as theselective formation of the contact.
 11. The method of claim 1 whereinthe contact regions and substrate comprise at least one of silicongermanium and gallium arsenide.
 12. A method of selectively formingcontact regions on a substrate including a plurality of exposed regions,the method comprising selectively forming a contact region on each ofthe exposed regions of the substrate, each contact region being formedhaving first and second surface portions, and during the selectiveformation of the contact regions, heating the first surface portion ofthe contact region relative to the second surface portion to increase agrowth rate of the region in a direction substantially perpendicular tothe first surface portion relative to a growth rate of the siliconregion in a second direction substantially perpendicular to the secondsurface portion.
 13. The method of claim 12 wherein the substratecomprises a silicon substrate and each of the contact regions comprisesa silicon region.
 14. The method of claim 13 wherein each of the siliconregions comprises an epitaxial region.
 15. The method of claim 12wherein the first surface portion corresponds to a horizontal surface ofthe contact region that is substantially parallel to a surface of thesubstrate, and the second surface portion corresponds to a verticalportion of the contact region that is substantially perpendicular to thehorizontal surface.
 16. The method of claim 12 wherein the methodfurther comprises forming an insulating layer on the substrate andremoving portions of the insulating layer to form the exposed regions ofthe substrate.
 17. The method of claim 12 wherein heating the firstsurface portion of the contact region comprises illuminating the firstsurface portion of the contact region with electromagnetic radiation toincrease the temperature of the first surface portion relative to thesecond surface portion.
 18. The method of claim 17 wherein the firstsurface portion of each contact region comprises an upper surface andthe second surface portion of the contact region comprises a sidewallsurface, the sidewall surface being substantially perpendicular to theupper surface, and the electromagnetic radiation having a direction ofpropagation that is substantially perpendicular to the upper surface andparallel to the sidewall surfaces to illuminate the upper surface andsubstantially not illuminate the sidewalls so that the temperature ofthe upper surface increases relative to the temperature of thesidewalls.
 19. The method of claim 17 wherein illuminating the firstsurface portion of the contact region with electromagnetic radiationcomprises applying collimated light to the portion.
 20. The method ofclaim 19 wherein the collimated light comprises a scanning laser beamapplied to the portion.
 21. The method of claim 12 wherein heating thefirst surface starts at substantially the same time as the selectiveformation of the contact.
 22. The method of claim 12 wherein the contactregions and substrate comprise at least one of silicon germanium andgallium arsenide.
 23. A method of enhancing the vertical growth ofregions being selectively formed on exposed regions of a semiconductorsubstrate, the method comprising selectively forming a region on each ofthe exposed regions of the substrate, each region being formed having ahorizontal surface and a vertical surface, and during the selectiveformation of the region, illuminating substantially only the horizontalsurface of the region with electromagnetic radiation to increase avertical growth rate of the region in a vertical direction substantiallyperpendicular to the horizontal surface relative to a horizontal growthrate in a direction substantially perpendicular to the vertical surface.24. The method of claim 23 wherein each of the regions comprises asilicon region.
 25. The method of claim 24 wherein each of the siliconregions comprises an epitaxial region.
 26. The method of claim 23wherein illuminating substantially only the horizontal surface of thesilicon region comprises applying collimated light to the horizontalsurface.
 27. The method of claim 26 wherein the collimated lightcomprises a scanning laser beam.
 28. The method of claim 23 whereinilluminating substantially only the horizontal surface of the siliconregion with electromagnetic radiation starts at substantially the sametime as the selective formation of the contact.
 29. The method of claim23 wherein the contact regions and substrate comprises at least one ofsilicon germanium and gallium arsenide.
 30. An integrated circuitcomprising a semiconductor substrate including a plurality oftransistors, each transistor including a pair of doped regions formedwithin the substrate and having a channel region defined between thedoped regions, and each transistor including a control stack formed overthe channel region, the integrated circuit including contactsselectively formed on each doped region, each contact being selectivelyformed and while each contact is being selectively formed, the contactbeing heated to increase a vertical growth rate of the contact relativeto a horizontal growth rate of the contact so that each contact has aheight greater than or equal to a height of the control stack whilebeing isolated from an adjacent contact being formed on a doped regionof an adjacent transistor.
 31. The integrated circuit of claim 30wherein the integrated circuit comprises an dynamic access randommemory.
 32. The integrated circuit of claim 30 wherein each transistorcomprises a MOS transistor.
 33. The integrated circuit 32 wherein thecontrol stack of each MOS transistor comprises a gate stack including anoxide layer, polysilicon layer, silicide layer, another oxide layer, anda nitride layer.
 34. The integrated circuit of claim 30 wherein thecontact is heated by illuminating an upper surface of the contact withelectromagnetic radiation.
 35. The integrated circuit of claim 34wherein the electromagnetic radiation collimated light.
 36. Theintegrated circuit of claim 35 wherein the collimated light comprises ascanning laser beam.